1. Field of the Invention
This invention relates to golf balls (including solid golf balls and wound golf balls).
2. Prior Art
The most requisite characteristic for golf balls is a long flight distance. When run is taken into account, golf balls traveling a low trajectory are mostly advantageous with respect to the total flight distance. Many golf balls having low trajectory performance have been proposed.
In general, an approach of deepening dimples is employed in order to provide low trajectory golf balls. However, such dimples intended for low trajectory suffer from the problem that the flight distance largely varies depending on manufacturing variances. Also, the angle of elevation largely varies with a slight difference of dimples. It is thus difficult to produce in a consistent manner golf balls which are satisfactory in carry.
In the prior art, various proposals were made regarding the overall dimple volume and other indexes associated with the design of dimples. The optimum value of these indexes can largely differ depending on the arrangement of dimples and the combination of large and small dimples. The optimizing efforts in the development of low trajectory-oriented dimples encounter many difficulties. A vast number of working steps and great expenses are needed for the development.
Therefore, an object of the invention is to provide a golf ball having low trajectory-oriented dimples with stable performance.
Making extensive investigations in order to achieve the above object and analyzing numerous data, the inventor has discovered that the sum of dimple trajectory volumes each obtained by multiplying a dimple volume by the square root of a dimple diameter (or total dimple trajectory volume) governs the angle of elevation of a ball when hit at a high head speed. By adjusting the total dimple trajectory volume to an optimum value, the variation in flight performance of the ball can be minimized. Additionally, by adjusting the dimple cross-sectional shape area ratio to be defined later to an optimum value, low trajectory-producing dimples ensuring a stretching flight in that the carry can be further extended even at the same angle of elevation are developed. It has also been found that better results are obtained by optimizing the number of dimples, the gage and hardness of the cover, and the hardness of the ball.
Accordingly, the invention provides a golf ball as defined below.
(1) A golf ball having a plurality of dimples formed in its surface, characterized in that the sum of dimple trajectory volumes each obtained by multiplying a dimple volume by the square root of a dimple diameter is 580 to 750, and the ball has a diameter of 42.67 to 42.97 mm.
(2) The golf ball of (1) wherein the elevational cross-sectional shape of the dimple at its center has an area S1, multiplying the dimple diameter by a dimple depth gives an area S2, the average of the dimple cross-sectional shape area ratios represented by S1/S2 is 0.61 to 0.68, and at least 80% of the entire dimples have a dimple cross-sectional shape area ratio of from 0.61 to 0.68.
(3) The golf ball of (1) or (2) wherein the total number of dimples is 360 to 540.
(4) The golf ball of (1), (2) or (3) comprising an outermost cover having a gage of 1.0 to 2.0 mm and a Shore D hardness of 38 to 50.
(5) The golf ball of any one of (1) to (4) comprising a cover of a multilayer structure, wherein a cover layer disposed next to the outermost cover layer has a gage of 1.0 to 2.0 mm, and the ball experiences a compression deformation of 2.6 to 3.4 mm when the load which varies from an initial load of 10 kg to a final load of 130 kg is applied to the ball.